We report new measurements of the production cross sections of pairs of charged pions and kaons as a function of their fractional energies using various fractional-energy definitions. Two different ...fractional-energy definitions were used and compared to the conventional fractional-energy definition reported previously. The new variables aim at either identifying dihadron cross sections in terms of single-hadron fragmentation functions, or to provide a means of characterizing the transverse momentum created in the fragmentation process. The results were obtained applying the updated initial-state radiation correction used in other recent Belle publications on light-hadron production cross sections. In addition, production cross sections of single charged pions, kaons, and protons were also updated using this initial-state radiation correction. The cross sections are obtained from a 558 fb-1 data sample collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider.
A
bstract
We present the analysis of two-particle angular correlations using coordinate systems defined with the conventional beam axis and the event thrust axis. We propose the latter as a good ...representation for the correlation structure interpretation in the
e
+
e
−
collision system. The
e
+
e
−
collisions to hadronic final states at center-of-mass energies of
s
= 10
.
52 GeV and 10.58 GeV are recorded by the Belle detector at KEKB. In this paper, results on the first dataset are supplementary to the previous Belle publication
1
. At the same time, the latter is the first two-particle correlation measurement at collision energy on the
Υ
(4
S
) resonance and is sensitive to its decay products. Measurements are reported as a function of the charged-particle multiplicity. Finally, a qualitative understanding of the correlation structure is discussed using a combination of Monte Carlo simulations and experimental data.
We study the decay B+→K+K– π+ and investigate the angular distribution of K+K– pairs with invariant mass below 1.1 GeV / c2. This region exhibits both a strong enhancement in signal and very large ...direct CP violation. We construct a coherent sum model for the angular distribution of the S- and P-wave, and report the ratio of their amplitudes, the relative phase and the forward-backward asymmetry. We also report absolute differential branching fractions and direct CP asymmetry for the decay in bins of MK+K– and the differential branching fractions in bins of MK+π–. The results are based on a data sample that contains 772 × 106 $B\bar{B}$ pairs collected at the $Υ$(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e– collider. The result favors the presence of S- and D-waves in low MK+K– region to the detriment of a P-wave.
A
bstract
We report a search for the charged-lepton flavor violation in Υ(2
S
) →
ℓ
∓
τ
±
(
ℓ
=
e, μ
) decays using a 25 fb
−
1
Υ(2
S
) sample collected by the Belle detector at the KEKB
e
+
e
−
...asymmetric-energy collider. We find no evidence for a signal and set upper limits on the branching fractions (
B
) at 90% confidence level. We obtain the most stringent upper limits:
B
(Υ(2
S
)
→ μ
∓
τ
±
)
<
0
.
23
×
10
−
6
and
B
(Υ(2
S
)
→ e
∓
τ
±
)
<
1
.
12
×
10
−
6
.
We study B+ → π+π0π0 using 711 fb-1 of data collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. Here we measure an inclusive branching fraction of ...(19.0 ±1.5 ±1.4)×10-6 and an inclusive CP asymmetry of (9.2 ±6.8 ±0.7)%, where the first uncertainties are statistical and the second are systematic, and a B+ → ρ(770)+π0 branching fraction of (11.2 ± 1.1 ± 0.9 $^{+0.8}_{-1.6}$)× 10-6, where the third uncertainty is due to possible interference with B+ → ρ(1450)+π0. We present the first observation of a structure around 1 GeV/c2 in the π0π0 mass spectrum, with a significance of 6.4σ, and measure a branching fraction to be (6.9 ±0.9 ±0.6) × 10-6. We also report a measurement of local CP asymmetry in this structure.
We measure the branching fractions and CP asymmetries for the singly Cabibbo-suppressed decays $D^0 → π^+π^-η, D^0 → K^+K^-η$, and $D^0 → Φη$, using 980 fb-1 of data from the Belle experiment at the ...KEKB e+e- collider. We obtain $$\mathcal{B}(D^0 → π^+π^-η = \mathrm{1.22 ± 0.02 (stat) ± 0.02(syst) ± 0.03}(\mathcal{B}_{\mathrm{ref}}) \mathrm{x 10^{-3}}$$ $$\mathcal{B}(D^0 → K^+K^-η = \mathrm{1.80^{+0.07}_{-0.06}(stat) ± 0.04 (syst) ± 0.05}(\mathcal{B}_{\mathrm{ref}}) \mathrm{x 10^{-4}}$$ $$\mathcal{B}(D^0 → Φη = \mathrm{1.84 ± 0.09 (stat) ± 0.0 (syst) ± 0.05}(\mathcal{B}_{\mathrm{ref}}) \mathrm{x 10^{-4}}$$ where the third uncertainty ($\mathcal{B}_{\mathrm{ref}}$) is from the uncertainty in the branching fraction of the reference mode $D^0 → K^-π^+η$. The color-suppressed decay $D^0 → Φη$ is observed for the first time, with very high significance. The results for the CP asymmetries are $$A_{CP} (D^0 → π^+π^-η) = \mathrm{0.9 ± 1.2 (stat) ± 0.5 (syst)}\%$$ $$A_{CP} (D^0 → K^+K^-η) = \mathrm{-1.4 ± 3.3 (stat) ± 1.1 (syst)}\%$$ $$A_{CP} (D^0 → Φη) = \mathrm{-1.9 ± 4.4 (stat) ± 0.6 (syst)}\%$$ The results for $D^0 → π^+π^-η$ are a significant improvement over previous results. The branching fraction and ACP results for $D^0 → K^+K^-η$, and the ACP result for $D^0 → Φη$, are the first such measurements. No evidence for CP violation is found in any of these decays.
A
bstract
The first dedicated search for the
η
c
2
(1
D
) is carried out using the decays
B
+
→ η
c
2
(1
D
)
K
+
,
B
0
→
η
c
2
(1
D
)
K
S
0
,
B
0
→ η
c
2
(1
D
)
π
−
K
+
, and
B
+
→ η
c
2
(1
D
)
π
+
K
...S
0
with
η
c
2
(1
D
)
→ h
c
γ
. No significant signal is found. For the
η
c
2
(1
D
) mass range between 3795 and 3845 MeV
/c
2
, the branching-fraction upper limits are determined to be ℬ(
B
+
→ η
c
2
(1
D
)
K
+
)
×
ℬ(
η
c
2
(1
D
)
→ h
c
γ
)
<
3
.
7
×
10
−
5
, ℬ(
B
0
→ η
c
2
(1
D
)
K
0
)
×
ℬ(
η
c
2
(1
D
)
→ h
c
γ
)
<
3
.
5
×
10
−
5
, ℬ(
B
0
→ η
c
2
(1
D
)
π
−
K
+
)
×
ℬ(
η
c
2
(1
D
)
→ h
c
γ
)
<
1
.
0
×
10
−
4
, and ℬ(
B
+
→ η
c
2
(1
D
)
π
+
K
S
0
)
×
ℬ(
η
c
2
(1
D
)
→ h
c
γ
)
<
1
.
1
×
10
−
4
at 90% C.L. The analysis is based on the 711 fb
−
1
data sample collected on the ϒ(4
S
) resonance by the Belle detector, which operated at the KEKB asymmetric-energy
e
+
e
−
collider.
Abstract We present a search for the dark photon A′ in the B 0 → A′A′ decays, where A′ subsequently decays to e + e − , μ + μ − , and π + π − . The search is performed by analyzing 772 × 106 B B ¯ $$ ...B\overline{B} $$ events collected by the Belle detector at the KEKB e + e − energy-asymmetric collider at the ϒ(4S) resonance. No signal is found in the dark photon mass range 0.01 GeV/c 2 ≤ m A′ ≤ 2.62 GeV/c 2, and we set upper limits of the branching fraction of B 0 → A′A′ at the 90% confidence level. The products of branching fractions, ℬ B 0 → A ′ A ′ × ℬ A ′ → e + e − 2 $$ \mathrm{\mathcal{B}}\left({B}^0\to A^{\prime }A^{\prime}\right)\times \mathrm{\mathcal{B}}{\left(A\prime \to {e}^{+}{e}^{-}\right)}^2 $$ and ℬ B 0 → A ′ A ′ × ℬ A ′ → μ + μ − 2 $$ \mathrm{\mathcal{B}}\left({B}^0\to A^{\prime }A^{\prime}\right)\times \mathrm{\mathcal{B}}{\left(A\prime \to {\mu}^{+}{\mu}^{-}\right)}^2 $$ , have limits of the order of 10 −8 depending on the A′ mass. Furthermore, considering A′ decay rate to each pair of charged particles, the upper limits of ℬ B 0 → A ′ A ′ $$ \mathrm{\mathcal{B}}\left({B}^0\to A^{\prime }A^{\prime}\right) $$ are of the order of 10 −8–10 −5. From the upper limits of ℬ B 0 → A ′ A ′ $$ \mathrm{\mathcal{B}}\left({B}^0\to A^{\prime }A^{\prime}\right) $$ , we obtain the Higgs portal coupling for each assumed dark photon and dark Higgs mass. The Higgs portal couplings are of the order of 10 −2–10 −1 at m h ′ ≃ m B 0 $$ {m}_{h\prime}\simeq {m}_{B^0} $$ ± 40 MeV/c 2 and 10 −1–1 at m h ′ ≃ m B 0 $$ {m}_{h\prime}\simeq {m}_{B^0} $$ ± 3 GeV/c 2.
The experimental results on the ratios of branching fractions R(D)=B(Bover ¯→Dτ^{-}νover ¯_{τ})/B(Bover ¯→Dℓ^{-}νover ¯_{ℓ}) and R(D^{*})=B(Bover ¯→D^{*}τ^{-}νover ¯_{τ})/B(Bover ¯→D^{*}ℓ^{-}νover ...¯_{ℓ}), where ℓ denotes an electron or a muon, show a long-standing discrepancy with the standard model predictions, and might hint at a violation of lepton flavor universality. We report a new simultaneous measurement of R(D) and R(D^{*}), based on a data sample containing 772×10^{6} BBover ¯ events recorded at the ϒ(4S) resonance with the Belle detector at the KEKB e^{+}e^{-} collider. In this analysis the tag-side B meson is reconstructed in a semileptonic decay mode and the signal-side τ is reconstructed in a purely leptonic decay. The measured values are R(D)=0.307±0.037±0.016 and R(D^{*})=0.283±0.018±0.014, where the first uncertainties are statistical and the second are systematic. These results are in agreement with the standard model predictions within 0.2, 1.1, and 0.8 standard deviations for R(D), R(D^{*}), and their combination, respectively. This work constitutes the most precise measurements of R(D) and R(D^{*}) performed to date as well as the first result for R(D) based on a semileptonic tagging method.
We present a new measurement of the Cabibbo-Kobayashi-Maskawa matrix element |Vcb| from B0→D*−ℓ+νℓ decays, reconstructed with the full Belle data set of 711 fb−1 integrated luminosity. Two form ...factor parametrizations, originally conceived by the Caprini-Lellouch-Neubert (CLN) and the Boyd, Grinstein and Lebed (BGL) groups, are used to extract the product F(1)ηEW|Vcb| and the decay form factors, where F(1) is the normalization factor and ηEW is a small electroweak correction. In the CLN parametrization we find F(1)ηEW|Vcb|=(35.06±0.15±0.56)×10−3, ρ2=1.106±0.031±0.007, R1(1)=1.229±0.028±0.009, R2(1)=0.852±0.021±0.006. For the BGL parametrization we obtain F(1)ηEW|Vcb|=(34.93±0.23±0.59)×10−3, which is consistent with the world average when correcting for F(1)ηEW. The branching fraction of B0→D*−ℓ+νℓ is measured to be B(B0→D*−ℓ+νℓ)=(4.90±0.02±0.16)%. We also present a new test of lepton flavor universality violation in semileptonic B decays, B(B0→D*−e+ν)B(B0→D*−μ+ν)=1.01±0.01±0.03. The errors quoted correspond to the statistical and systematic uncertainties, respectively. This is the most precise measurement of F(1)ηEW|Vcb| and form factors to date and the first experimental study of the BGL form factor parametrization in an experimental measurement.
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